The present invention relates to a surveying instrument for measuring distance, level, azimuth or the like.
Heretofore, collimation of a surveying instrument is carried out by directing an optical axis (referred to as a collimation axis hereinafter) of a telescope, and peering through the telescope so as to bring the central point of an object in the field of view to be coincident with the intersection of cross hairs on the collimation axis.
However, the position of an observer's eye with respect to an ocular lens varies depending upon the direction of observation, an observer's ability, degree of fatigue of observer or the like, as a result of which even if the adjustment of the telescope in the collimation axis direction is carried out accurately, there may occur an error for every surveying. Furthermore, the above-mentioned adjustment has been carried out manually and therefore it may be somewhat difficult to make the accuracy of the adjustment constant for every surveying depending upon the observation direction, the observer's ability, the degree of fatigue of the observer or the like, similar to the above, resulting in worsening of the surveying error.
Moreover, since the surveying is carried out by visual observation, the surveying becomes difficult when the object is dimly lit.